Ultra high frequency generator



July 6, 1943. 5 O

ULTRA HIGH FREQUENCY GENERATOR Filed March 6, 1941 Ewe/WW6: i (M,

erator embodying the Patented July 6, 1943 7 2,323,613 ULTRA HIGH FREQUENCY GENERATOR Fritz Liidi, Baden, Switzerland, assignor, by

mesne assignments, to Patelhold Patentverwertungs '& Elektro-Holding A. G.. Glarus, Switzerland, a; joint stock company Application March 6, 1941, Serial No. 382,089 In Switzerland February 20, 1940 7 Claims. (Cl. 25036) Ultra short wave generators which operate on the phase focussing principle are known per se. In order to produce ultra high frequency oscillations a velocity variation in accordance with an ultra high frequency cycle is impressed in a modulator on an electron beam having an initial homogeneous velocity. As a result of these periodic velocity variations more or less definitegroups of electrons occur behind the modulator,

these depending upon the distance traversed and producing alternating voltages of ultra high frequency in a so-called inductor which is-located sufiiciently far away from the modulator... In

order to obtain self-excitation of the generator the modulator, both circuits being coupled together over a high frequency conductor. The high frequency produced is then transmitted to the ultra high frequency load by means of an additional high frequency conductor which is coupled to the oscillation circuit connected with the inductor.

When compared with generators of the foregoing kind, according to the present invention in an ultra short wave generator operating on the phase focussing principle, a feed-back arrangement is employed which has only-a single electrical resonator which is connected to the inductor and the modulator in such a manner that the amplitude of the ultra frequency voltage at the modulator is smaller than at the inductor, means being also provided to couple an ultra high frequency load to the resonator providing the feed-back The ultra short wave generator according to the invention when com-, pared with the ultra short wave generators known up to the present and also operating with phase focussing of the electron beam, possess'es important advantages which are referred to in greater detail in the following description of constructional examples which are illustrated diagrammatically in the accompanying drawing.

' In the drawing: Fig. l is a longitudinal section through a genprinciples of the invent n; I

-Figi2 is a transverse section on line 2-72. of Fig. 1, and Fig. 3 is a transverse section on line 33 of Fig.1.

e In the constructional example shown in Fig. 1

the cathode 2 which is heatedby a filament l is from the modulator 5.

enclosed in a Wehnelt cylinderfl. This Wehnelt. cylinder 3 combined with a grid ordiaphragm type of accelerating electrode 4 enables the stream of electrons to form a sharply defined beam. This electron beam which attains a velocity corresponding to the potentialof the ac-f celerating electrode first passes through the socalled modulator 5 which in this case consists of two grid shaped electrodes ,6 and 7. Since ultra high frequency voltages prevail between the electrodes 6 and l the electron beam leaving the modulator no longer has a homogeneous velocity with regard to time but is given a variable velocity-which follows the rhythm of the ultra high frequency control voltages. After a certain distance has been traversed relatively sharply defined electron groups are formed which re-f combine again at a still greater distance away The place where these. electron; groups are most noticeable is thus termed the focus. The inductor 8 is preferably located at this focus and also consists of two grid shaped perforated electrodes 9 and It). The electrons passing through the inductor 8 transfer a large part of their kinetic energy to it and generate ultra high frequency alternating voltages at both of its'electrodes 9 and Ill which can be fed back to the modulator so that the entire device operates as a self-excited generator. The electrons are thereupon caught by an anode H which like the accelerating electrode 5 is connected to the positive terminal of a direct current voltage source not shown in the drawing. It is expedient if the accelerating electrode 4, the electrodes 6 and '7 of the modulator 5, the electrodes 9 and iii of the inductor 8, and the anode I! all receive the same direct voltage potential relative to the cathode 2. The Wehnelt cylinder can be connected either directly with the cathode or receive a suit able positive or negative bias voltage relative to that of the cathode.

In connection with the operation of agenerator of this kind it should be noted that the position of the focus depends on the one hand on the accelerating voltage at the electrode l and on the other hand also on the magnitude of the effective ultra high frequency control voltage at the modulator electrodes 6 and 1. Furthermore the phase of the alternating voltage produced at the inductor electrodes 9 and H] with reference to the control voltage at the modulator is fixed by the transit times of the electrons in passing from the modulator 5 to the inductor 8. In order to'obtain a feed-back with the correct phase under such conditions, an oscillation circuit with as small a clamping as possible is applied to both the inductor electrodes 9 and I and the modulator electrodes 6 and I, both of these oscillation circuits being coupled together by means of a special coupling loop. If the resonance frequencies of both oscillation circuits are made variable and an adjustment is provided in the coupling loop, it is possible to vary the phase angle of the transmission factor of this band. filter within a comparatively broad frequency band for the frequencies provided. It is therefore always possible when employing such a feed-back circuit to comply with the feed-back conditions necessary for self-excitation with a definite or fixed frequency. In order to obtain with ultra high frequencies sufficiently high resonance resistances in both oscillation circuits, toroid shaped hollow-space resonators have been used which are coupled together by means of a concentric pipe conductor. The aforementioned adjusting devices result, however, in a very complicated assembly when applied to such constructions, micrometer screws being required in order to obtain a correct adjustment. It is also undesirable that adjusting devices have to be located inside the vacuum space and be operated from outside.

The object of the present invention is to avoid these drawbacks which the known forms of construction possess and also to improve the efficiency of such generators. Although with the known kinds of generators the feed-back condition can be fulfilled by means of the two oscillation circuits and the correct phase adjusted to suit the prescribed operating conditions, the amount of feed-back is subject to large fluctuations when the phase is being adjusted, so that the conditions for maximum power output are not always fulfilled.

When the oscillation circuits are coupled, the amount of the external feed-back at which the correct phase results will often be equal to or even greater than unity, this being especially the case when the circuits are mutually out of tune. Under such conditions the modulator and inductor will have practically equally large amplitudes. Since, however, the distance of the focus decreases when the amplitude increases and lies in the vicinity of the inductor if the feed-back conditions are fulfilled, a high emciency cannot be obtained on account of the limitation thus imposed on the high frequency amplitude.

If, however, the inductor and modulator electrodes shown in Fig. 1 are coupled by means of only a single oscillation system it is easily pos sible to satisfy both the conditions required for self-excitation and high efiiciency. In Fig. 1 the oscillation system consists of a Lecher system with the two parallel conductors l2 and I3. Each of the conductors l2 and 13 connects by means of brackets l4, 15, Hi and II respectively an inductor electrode with a modulator electrode. In order to avoid detrimental reflection places in a design of this kind, at least that part of the Lecher line which connects the inductor with the modulator should be located within the vacuum space contained in the vacuum vessel 1 8. Both conductors l2 and !3 are thus located so as to be parallel to the direction of the electron beam which is indicated in the drawing by the broken lines. To prevent the electron beam from being deflected in a transverse direction by the electric field prevailing between the Lecher conductors l2 and [3, these latter are located away from the tube axis more towards the tube wall which is made of insulatin material such as glass or the like.

Figs. 2 and 3 illustrate cross-sections of the generator shown in Fig. 1, Fig. 2 being a section on the line a-a as seen from the left and Fig. 3 a section on the line bb. These figures show plainly that the electron beam which passes through the grid-shaped electrodes land 6 is outside of the plane joining the conductors l2 and i3 and therefore all transverse deflection is substantially avoided. To ensure that the Lecher system is slightly damped, the electrical connection on at least one side is located in the vacuum space. This can occur at either a voltage node or antinode. The arrangement shown in Fig. 1, is however, the most advantageous, the Lecher system l2, l3 ending in this case on both sides at a voltage node. The ends of the two wires l2 and i3 are thus connected to two circular metal discs located in the glass tube l8, one of which acts as the acceleration electrode 4 and the other as the anode H. The disc 4 acting as the acceleration electrode has a central opening in which there are grid bars similar to those of the electrodes of the modulator 5 and the inductor 3, these bars being shown in section in Fig, l. The distance between the discs 4 and l l is made equal to about half the wave length to be generated and the electrodes 9 and [0 are located midway between the discs 4 and ll, that is say connected at a point coinciding approximately with a voltage antinode. Since excitation of the fundamental wave is preferred, the coupling of the modulator shown in the drawing will necessarily produce a considerably smaller amplitude at the modulator electrodes than at the inductor electrodes, so that it is thus possible to fulfill the feed-back conditions merely by altering the acceleration voltage. If for instance the peak value of the ultra high frequency voltage produced at the inductor has nearly attained the same value as the acceleration voltage, it is always possible to feed back a voltage to the modulator which displaces the focus of the phase-modulated electron beam to the point where the inductor is located, so that maximum efiiciency is achieved. If, however, as in the known kinds of tubes, the entire alternating voltage of the inductor were to be fed back to the modulator, the focus at the given peak value of the alternating voltage would not be displaced to the inductor but to the modulator, that is to say the oscillations would be prematurely interrupted or in other words a considerably smaller peak value would be obtained for the high frequency than that limited by the acceleration value, this being equivalent to a lower efiiciency.

The simple assembly of the tube as shown in Fig. 1 is particularly advantageous, this being especially the case as regards the smaller sealedoif generators. An ultra high frequency load such as an antenna can be very easily coupled to the generator. In order to facilitate connection with a working circuit both wires I2 and I3 of the Lecher system, as shown in Fig. 2 can be located in the vicinity of the tube wall and the circuit connected by means of a coupling loop located outside the tube. It is preferable to connect up to a power line 29 (Fig. 3) also consisting of a parallel wire system, this latter being led through the tube envelope and being directly connected to the Lecher wires I2, I3 of the feedback. By these known means the correct adjustment between load and generator is obtained.

I claim:

1. An ultra short wave generator comprising means for generating an electron beam in an evacuated space, a modulator comprising a pair of grid electrodes positioned in said beam for subjecting the beam to ultra high frequency potential variations whereby ultra high frequency velocity variations are produced in the beam, an inductor comprising a pair of grid electrodes positioned in the modulated beam whereby ultra high frequency alternating voltages are produced in said inductor, and a feed-back connection between said modulator and said inductor comprising a single resonator to which the ultra high frequency load is connected, said resonator comprising a Lecher system which is electrically terminated at at least one end, both conductors of the Lecher system being each connected to an inductor and a modulator electrode and being positioned parallel to the electron beam with the plane passing through both conductors outside said beam.

2. An ultra short wave generator as defined in claim 1 in which at least that part of the Lecher system which connects the inductor and the modulator being located within the vacuum space of the generator.

3. An ultra short wave generator comprising means for generating an electron beam in an evacuated space, a modulator comprising a pair of grid electrodes positioned in said beam for subjecting the beam to ultra high frequency potential variations whereby ultra high frequency velocity variations are produced in the beam, an inductor comprising a pair of grid electrodes positioned in the modulated beam whereby ultra high frequency alternating voltages are produced in said inductor, and a feed-back connection between said modulator and said inductor comprising a single resonator to which the ultra high frequency load is connected, said resonator comprising a Lecher system located entirely within the evacuated spac of the generator and terminating at one end at a voltage node with an accelerating electrode and terminating at the other end at a voltage node with an anode.

4. An ultra short wave generator as defined in claim 3 in which the length of the Lecher system corresponds to half the wave length to be generated, and the electrodes of the inductor are located at the center of the Lecher system and connected thereto at a voltage antinode.

5. An ultra short wave generator comprising means for generating an electron beam in an evacuated space, a modulator comprising a pair of grid electrodes positioned in said beam for subjecting the beam to ultra high frequency potential variations whereby ultra high frequency velocity variations are produced in the beam, an inductor comprising a pair of grid electrodes positioned in the modulated beam whereby ultra high frequency alternating voltages are produced in said inductor, and a feed-back connection between said modulator and said inductor comprising a single resonator to which the ultra high. frequency load is connected, said resonator comprising a Lecher system which is electrically terminated at at least one end, both conductors of. the Lecher system being each connected to an in-- ductor and a modulator electrode and being po-- sitioned parallel to the electron beam with the plane passing through both conductors outside said beam and so near to a wall of the envelope enclosing the evacuated space that the ultrahigh frequency load can be inductively coupled to the generator by means of a coupling loop positioned outside the envelope.

6. An ultra short wave generator comprising means for generating an electron beam in an evacuated space, a modulator comprising a pair of grid electrodes positioned in said beam for subjecting the beam to ultra high frequency potential variations whereby ultra high frequency velocity variations are produced in the beam, an inductor comprising a pair of grid electrodes positioned in the modulated beam whereby ultra high frequency alternating voltages are produced in said inductor, and a feed-back connection between said modulator and said inductor comprising a single resonator to which the ultra high frequency load is connected, said resonator comprising a Lecher system which is electrically terminated at at least one end, both conductors of the Lecher system being each connected to an inductor and a modulator electrode and being positioned parallel to the electron beam with the plane passing through both conductors outside said beam and parallel conductor elements connecting the Lecher system with the ultra high frequency load through the envelope enclosing th evacuated space.

7. An ultra short wave generator comprising means for generating an electron beam in arr evacuated space, a modulator comprising a pair of grid electrodes positioned in said beam for sub-- jecting the beam to ultra high frequency potential variations whereby ultra high frequency velocity variations are produced in the beam, an. inductor comprising a pair of grid electrodes positioned in the modulated beam whereby ultra high frequency alternating voltages are produced in said inductor, and a feed-back connection between. said modulator and said inductor comprising av single resonator to which the ultra high frequency load is connected, said resonator comprising a Lecher system which is electrically terminated at at least one end, both conductors of the Lecher system being each connected to an inductor and a modulator electrode to provide a smaller amplitude of the ultra high frequency voltage at the modulator than at the inductor and being positioned parallel to the electron beam with the plane passing through both conductors outside said beam.

FRITZ LT jDI. 

